DE102006027132B4 - Method for detecting defects in concrete components - Google Patents

Abstract

A method for detection and classification of imperfections in components is proposed having the following stages: Irradiation of pulsed ultrasonic waves from electrical emission pulses on several points of the surface of the component to be examined, reception of the reflected ultrasonic waves at several points of the surface for generating multiple electrical reception signals, analysis and evaluation of the electrical reception signals in terms of their amplitude information with reference to the positions of the points of the irradiated ultrasonic waves and the detected reflected sound waves for generating a three-dimensional spatial distribution of the scattering properties of the component. In addition to the amplitude information, the phase angle of scattering readouts is evaluated and the phase information is assigned to the three-dimensional spatial distribution of the scattering properties of the component, with the amplitude information being invoked for detecting the imperfections, and the amplitude information and the phase information of the three-dimensional spatial distribution being invoked for classification.

Description

The The invention relates to a method for detecting defects in components, in particular of Verpressfehlern in clamping channels or of compaction defects in concrete components according to the preamble of the main claim.

Lots Concrete structures of the present are so-called prestressed concrete structures. There concrete has only a relatively low tensile strength, this is through an artificial one internal prestressing of the objects achieved by steel cables or tension wires. The steel cables are guided in so-called. Chutes or sheaths and after hardening the concrete stretched. Then the ducts are filled with grout to a strong bond between the steel cables and the concrete structure to reach. It is important that the grout the sheaths completely filled in and the tension wires gapless encased in moisture in cavities can accumulate and the tension wires through Corrosion attacked and destroyed can be. Such cavities or Verpressfehler in clamping channels represent a quality defect in extreme cases, to the failure of the component and collapse of the Building leads. To assess the stability of a concrete structure is as well the knowledge about compression defects and gravel nests essential.

to Detection of defects in components is the ultrasonic echo method known, in the ultrasonic waves in the surface of the object to be examined are irradiated and the reflected sound waves are detected. Depending on the intensity the reflection is closed to defects. The detection of prestressing relies on the intensity the reflection of the measuring surface facing the cladding tube side. with air bubbles this is significant compared to well compressed areas intensive (see Krause, M., Mielentz, F, Milmann, B., Strings, D., Müller, W., Ultrasonic imaging of concrete elements: State of the art using 2D synthetic aperture, in: DGZfP (Ed.): International Symposium of Non-destructive Testing in Civil Engineering (NDT-CE) in Berlin, Germany, September 16-19, 2003, Proceedings to BB 85-CD, V51, Berlin (2003); Kroggel, O .; Scherzer, J .; Jansohn, R .: The Detectability Of Improper Filed Ducts With Ultra-sound Reflection Techniques. NDT. net - March 2002, Vol. 03; Schickert, M .; Krause, M .; Miller, W .: Ultrasonic imaging of concrete elements using SAFT Reconstruction, Journal of Materials in Civil Engineering 15 (2003) 3, pp. 235-246). In addition, can the backside reflection of the cladding tube be used to interpret the Verpresszustandes, the only occurs in well-pressed sections.

Of the Invention is based on the object, a method for detection of defects in components to create that over the Ultrasonic echo method according to the prior art, the statement security improved in the detection of defects.

These The object is achieved by the characterizing features of the main claim in connection with the Characteristics of the preamble solved.

Thereby, that at a plurality of locations pulse-shaped ultrasonic waves in the concrete component are irradiated and the reflected ultrasonic waves also be taken in several places on the surface and subsequently the electrical reception signals using the positions the points of irradiation and recording to produce a three-dimensional Spatial distribution of the scattering properties of the object analyzed and be evaluated, in addition for amplitude information, the phase value of the scattering process, d. H. the phase information of the three-dimensional spatial distribution of Scattering properties of the object is evaluated and the defects are the Amplitude information and the phase information of the three-dimensional Location distribution of the scattering properties are located, the significance and statement assurance in the detection of defects, z. B. Pressing error significantly improved.

It Thus, the phase position together with the amplitude information the scattering process for the characterization of the condition of the component, for example used of the chip channel. Preferably, the amplitude and evaluated phase information with the help of reconstruction, since while the measurement data are better focused. This can be done manually by analyzing the graphical representation of the sections and projections from the three-dimensional local distribution or from the 2D or 3D SAFT reconstruction in the form of B-pictures and C-pictures or automated by calculation of the Phase value done. Such a procedure can also be used for detection of compaction defects and Gravel nests are applied in concrete, being evaluated by the evaluation the phase position these can be distinguished from rebars.

The inventive method allows automated data acquisition, evaluation and documentation, where raw data, reconstructions, geometry information and phase evaluation are object related be determined, visualized and stored.

in the The following is the method according to the invention using the attached Figures closer explained. Show it:

1 a perspective schematic view of a concrete component as a test specimen,

2 a representation of a section from the measurement data before the reconstruction,

3 an amplitude and phase representation of the three-dimensional reconstruction of the measurement data in the depth section,

4 an amplitude and phase representation of the three-dimensional reconstruction of the measured data in a section parallel to the measuring surface,

5 a construction plan of another example of a concrete component with cast-in metal and Styrodur plates,

6 a reconstruction of the measurement data in terms of amplitude as a section in the depth of the metal plates and

7 a reconstruction of the measurement data with respect to the phase as a section in the depth of the metal plates.

at the method according to the invention be ultrasonic waves over suitable ultrasonic transducers coupled into the concrete component and the at the back the concrete component or at defects, reinforcements and other material jumps reflected Ultrasonic waves are received by the ultrasonic transducers. Suitable ultrasonic transducers are, for example, those based on piezo working oscillators that do not require a coupling agent. It will be, for example used multiple arrayed in a single oscillator, the having resiliently mounted contact tips. It can be one or several of the single oscillators work as transmitters while the other than receiver serve. The received signals are transformed into processable digital data converted and saved. To examine the entire component to be able to The ultrasound measurement is done in a dense grid on the accessible surface performed the component. there Care must be taken that the measurement data is of high quality are. Furthermore become the transmitting and receiving positions of the ultrasonic transducer or sensors recorded and stored.

in the known prior art, the detected raw data, in terms of the amplitude of the received ultrasonic waves are meaningful, together with the position information of the ultrasonic sensors with a 3D imaging or imaging techniques, such as a 3D SAFT algorithm (Synthetic Aperture Focussing Technique), which increases the volume of the Component reconstructed in three dimensions and thus the interior of the Concrete components acoustically mapped and the spatial distribution of the scattering properties is pictured.

The Locating Verpressfehlern in span channels as a concrete embodiment is thus u. a. on the measurement of an intensity difference the reflection of ultrasonic pulses at the tendons, wherein at air inclusions, represent the Verpressfehler, virtually a total reflection takes place d. H. the reflection coefficient takes its maximum possible Value. Opposite is the reflection on well-pressed ducts lower, because parts of the sound through the thin one Cladding tube wall and the grout in the cladding tube penetration.

For the evaluation can thus from the three-dimensional reconstruction of the scattering properties Cuts and projections are derived as B-pictures and are known as C-pictures, wherein the C-pictures parallel to the Einstrahloberfläche (parallel to the XY plane) lie while the B-pictures cut planes through the material in the direction of the radiation are.

At These images can be the depth and intensity distribution of the reflection can be read from which in turn can be determined where There are errors. From standard reconstructions are in one selectable Depth raster the intensity distributions delivered. Then the coordinates are selected, in which a reflector discovered or expected. Overall, the visualization process is interactive.

to Safe location of injection errors is sufficiently clear Difference in reflection between well compressed and air filled area required. In practice, this is not always achieved because the Ultrasound propagation in addition the limp armor, the goodness the sound transmission on the concrete surface and the condition of the concrete is affected. Therefore, accordingly the invention for the evaluation in addition for amplitude information, d. H. to the intensity differences of reflection of ultrasound pulses within the component caused by the reflection caused phase change the ultrasonic pulses used, d. H. it will be the phase of considered reflected signal.

It It is known that a measured with a piezoelectric transducer ultrasonic pulse (Sound pressure) at a reflection on an acoustically denser material maintains its momentum while in the reflection at a boundary layer to a thinner material a phase jump of 180 °, that is, a momentum reversal, ie. H. in a reflection on steel the phase is maintained while in the air of the phase jump occurs.

There in concrete components the reflections are superimposed by different interfaces, wherein in the embodiment the transition of cladding tube wall or steel strand for grouting mortar each one addi tional Boundary layer is required, not just the phase jump of the reflected pulse but also the phase rotation, which results overall in a multi-layered system. The above outlined cases 0 ° and 180 ° phase position are special cases, which are easily understood by pulses and sinusoidal or cosinusoidal signals since a phase shift of 180 ° means a sign reversal for cosine functions: cos (phi) = - cos (phi + 180 °). A pulse-shaped signal let yourself decompose into spectral components, which in the case of ultrasonic excitation order a center frequency (bandpass signal), with each spectral component consists of a phase-shifted cosine function. It is actually the spectrum is continuous, d. H. there are all frequencies, but in a numerical spectral decomposition (discrete Fourier transformation DFT), discrete spectral lines are obtained. Will simplicity half only the spectral line at the center frequency of the probe considered, so heard plus a cosine oscillation with an amplitude and a phase angle. The phase relationship, however, refers to the start time of the Spectral analysis and this is freely selectable. Therefore, the phase position the spectral line and thus the phase angle of the analyzed pulse only determinable up to an offset. Since the phase position for the scattering process must be determined, not the start time of the transmission signal as Reference point are used, but a typical time in the received scattering pulse. With a symmetrical pulse can it is easy to "sit down" on the pulse peak and then identify the Peak as positive or negative and thus at 0 ° or 180 ° phase.

On the other hand is at impulses caused by scattering on non-flat surfaces, or At layers arise, always a superposition of many impulses available (at only one frequency would of interference), which is the symmetry of the total momentum change, and thus the determination of the reference point is no longer obvious and the analysis of the phasing becomes arbitrary.

in the Below, the difference between signal evaluation and reconstruction evaluation becomes better understanding shown. The above statements related to the measured Ultrasonic signal. Mapping techniques such as 3D JUICE, by a one-sided measuring surface go out, transfer the phase information (for lack of limited resolution) on the reconstruction and the signals are replaced by synthetically focused B-pictures. More specifically, the time coordinate in the signal is replaced by the depth coordinate in the reconstruction (in the embodiment the z-coordinate). The displayed phase value is not in both cases identical, but has the same tendency. This results from the complex structure of the SAFT algorithm, which causes some of the Phase rotation in the scattered signal partially corrected (scatterometry-dependent components) others but not (thin Layers, multiple reflections). The resolution in the reconstruction is essentially the same as the resolution in the depth direction Time signals, only the way (wavelength) with the help of the propagation speed umzunormieren. However, the focused B-picture is the reconstruction much smoother than the data, so the phase determination works better.

through An algorithm also becomes the phase of the reflected ultrasound pulses evaluated and based on a three-dimensional reconstruction calculated the phase information. The result is the Phase rotation during reflection in a color scale accordingly the B- or C-pictures, which makes it possible to determine the value of the phase rotation spatially resolved read.

To the current Time is used to determine the phase position of the scattering process as follows:

Phase determination from the pulse shape of the Reconstruction:

Method a):

It the depth scale from the amplitude maps is used and the waveform in the depth of an expected scattering process (top edge cladding tube o. Ä.) Considered and then recognize the sign of the main pulse.

Method b):

It becomes a mathematical envelope over the B-picture (or the Signal) - this is a kind of intensity value calculation - calculated, found in this way the center of the ad and at this point the Sign of the (unencumbered) original B image analyzed.

Computational method:

The envelope of the B-picture (or the signal) is calculated and the maximum of the envelope is defined as the phase reference point. From this point, the pulse is cut off a vibration of the center frequency to the right and to the left and determined via a Fourier transformation of this section of the phase value of the spectral line at the center frequency, which can now assume values of 0 ° -360 °. This value is the respective Allocated to scattering center. Thus, phase values are not obtained for the entire B-picture, but only for scattering centers. The selection of the scattering centers takes place via a threshold value of the envelope which can be set.

The Calculation was roughly described above; as parameters enter: wavelength at the center frequency, two cutting parameters for the width of the cut out Signal window and the threshold of the identification sensitivity. It is in the current implementation, the phase information for the entire Reconstruction is calculated and then the sections can be put together be displayed interactively with the amplitude information. Around to more easily grasp the geometric context in an image, is the amplitude image in the phase image as a black and white image for values smaller than the identification threshold with. This is the Phase information as a color value, the amplitude as the brightness value with contains, shown. Using cursors, the phase value can be used as a numerical value be displayed at every point of the reconstruction.

1 shows the schematic representation of a concrete component 1 as a test specimen with a cladding tube 2 , into the steel strands 3 drawn in and using grout 4 are fixed. An injection error 5 , ie an unpressed area is hatched. In the figure above is the measuring surface and in particular a measuring line 7 above the cladding tube 2 on the concrete component 1 and below in the same a limp armor 8th arranged. In the real component is usually a reinforcement layer also between cladding 2 and measuring surface 6 to find what is not considered here.

In the 2 to 4 the evaluation of the ultrasound waves irradiated and reflected into the test specimen is shown.

2 shows a section (B-picture) of the surface measurement along a line over the cladding tube 2 in the x-direction for y - 0.67 m, ie the time tx 10 ⁴ s above the location x in m. From the course of the amplitude of the measurement signals it can be seen that a pulse deformation in a region of the cladding tube 2 occurs, which was manufactured as unpressed. Although it is also a change in amplitude to recognize, but also of the limp reinforcement between cladding 2 and measuring surface could arise (in fact, such an area exists in the specimen).

3 shows above the amplitude and below the phase evaluation of the 3D-FT-SAFT reconstruction of the measured data 2 as a B-picture, ie as a depth-cut x, z at y = 0.7 m. Analysis of the data shows that the phase provides distinctly different values between compressed and unpressed area (about 150 ° vs. 86 °). Since the figns can not be displayed as color images, they are displayed as black and white images with additional hatchings of the relevant displays and labeled.

4 shows a slice (C-picture, x, y) of the 3D-FT-SAFT reconstruction of the measurement data of the 2 with regard to the evaluation of the amplitude (top) and the phase (bottom) parallel to the measuring surface in the depth of the upper edge of the cladding tube 2 (z = -0.285 m). Again, the non-compressed area is clearly visible.

In 5 is another example of a specimen, namely a plate specimen from the back and shown in section, which has a plurality of metal plates 1, 2 and 4 to 6 different thickness, which are cast in concrete under application of Styrodur A, which is intended to represent air. Field 3 is filled with concrete and Styrodur without metal. The places without Styrodurverbund are designated B. SPK1 and SPK2 are clamping channels that lie behind the metal plates.

The in the 6 and 7 Reconstructions indicated are cuts at a depth of about 10 cm, ie seen in the depth of the upper edges of the metal plates from the front. The Styrodur plates A are located under the metal plates and depending on the respective thicknesses of the same at different depths. Because of the resolution of the reconstruction Styrodurplatten A are behind the thin sheets (metal plates) to see in the plane thereof. For thick metal plates, however, they are outside the illustrated depth range. The styrodur plate in the area 3 Without metal plate has slipped out of the situation during production and is also outside the displayed range. 6 is a SAFT reconstruction of measurement data regarding the amplitude of the concrete part 5 , In the evaluation clearly echo displays of interfaces are visible. More precise statements about the type of interface, such as solid / solid or solid / gaseous (in this case concrete / steel or steel / air inclusion) can not be made. 7 is the reconstruction of the phase, whereby the phase of the reflected impulses now provides information about the type of interfaces. The visual recognition is based on a representation of different colors, which are provided here in black / white or different gray levels.

The designations in 5 are as follows:

1

Sheet steel, d = 2 min

2

Sheet steel, profiled, d = 0.5 mm

3

concrete B35, 16 min largest grain

4

Sheet steel, d = 15 mm

5

Sheet steel, d = 0.5 mm

6

Sheet steel, d = 40 mm

A

Stypodur (48 mm)

B

without composite

SPK 1 and SPK 2

chip channel (6 strands)

Claims (6)

Method for detecting defects in components, in particular of compression errors in chip channels or compaction defects in concrete components, comprising the following steps: irradiating pulsed ultrasonic waves from electrical transmission pulses at several points on the surface of the component to be examined, recording the reflected ultrasonic waves at several points of the surface for generation a plurality of received electrical signals, evaluating the received electric signals by using the positions of the locations of the irradiated ultrasonic waves and the received reflected sound waves to produce a three-dimensional location distribution of the scattering characteristics of the component and analyzing the three-dimensional location distribution of the scattering characteristics with respect to the amplitude information, characterized in that in addition to the amplitude information of the three-dimensional spatial distribution of the scattering properties of the component, the phase is analyzed and the defects are detected and determined on the basis of the analysis of the amplitude information and the phase information of the three-dimensional spatial distribution of the scattering properties. Method according to claim 1, characterized in that that the irradiation and recording of ultrasonic waves in one dense grid on the surface performed the component becomes. A method according to claim 1 or claim 2, characterized characterized in that the amplitude information and the phase information obtained using a 3D imaging technique, such as the 3D SAFT algorithm analyzed three-dimensional spatial distribution of the scattering properties and evaluated. Method according to one of claims 1 to 3, characterized that from the three-dimensional spatial distribution of the scattering properties Cuts and projections are depicted, with the Amplitude information and the phase information in each case in color or in grayscale in the representations of the cuts and projections are included. Method according to one of claims 1 to 4, characterized that analysis using signed B-pictures and C-pictures carried out becomes. Method according to one of claims 1 to 5, characterized that compression error in span channels and / or compaction defects and gravel nests in concrete components are detected and classified.